This invention relates to automobile passive restraint safety devices and, more particularly, to pyrotechnic gas generator units for inflating automobile airbags.
Large numbers of people are killed or injured annually in automobile accidents wherein the driver and/or passengers are thrown forward so as to impact against solid surfaces within the vehicle. Consequently, there has been considerable development of passive restraint systems for use with these vehicles. The term xe2x80x9cpassivexe2x80x9d means that the driver or passenger need not do anything to benefit from the device, as opposed to seat belts which are considered to be an xe2x80x9cactivexe2x80x9d restraint system. One system which has been extensively investigated senses rapid deceleration of the vehicle such as that which occurs upon a primary impact between an automobile and, for example, another car. It thus initiates inflation of a bag between the interior surface of the car and the vehicle occupant prior to the occurrence of any secondary collision between the driver and/or passengers and the interior of the car. Airbags have been in widespread use for more than a decade, but accounts of injuries and fatalities caused by their explosive deployment have raised concerns about their safety. Airbag inflation speeds of nearly 200 miles per hour or more are common to compensate for the driver""s or the passenger""s forward motion during a frontal impact. Inflation of the bag must therefore occur within milliseconds of the primary impact in order to restrain any occupants before they are injured due to secondary collisions against the solid surfaces within the vehicle
As noted above, there are in the prior art various devices which cause a protective bag to inflate in front of an automobile driver or passenger to cushion the impact with the steering wheel, dashboard or other interior vehicle surface. Usually the device is activated by an inertial switch responsive to a primary crash impact. This inertial switch in turn causes an inflator apparatus to quickly inflate a collapsed bag into a protective position in front of the driver or passenger.
The inflating gas is generally supplied either from a source of compressed air or other compressed gas, such as shown in Chute, U.S. Pat. No. 3,411,808 and Wissing et al., U.S. Pat. No. 3,413,013, and a number of other patents in the crash restraint field. In several other prior art patents (e.g., U.S. Pat. No. 3,880,447 to Thorn et al.; U.S. Pat. No. 4,068,862 to Ishi et al.; U.S. Pat. No. 4,711,466 to Breed; and U.S. Pat. No. 4,547,342; U.S. Pat. No. 4,561,675 and U.S. Pat. No. 4,722,551 to Adams et al.), the bag is inflated by igniting a pyrotechnic propellant composition and directing the gaseous combustion products produced thereby directly into the bag.
The first technique discussed above for inflating an airbag requires a reservoir of gas stored at a very high pressure, which may be discharged into the bag as soon as an impact is sensed. In order to obtain a sufficient volume of gas for inflating a vehicle occupant restraint bag, however, a relatively large reservoir of gas, at pressures of 3000 psi or more is required. To open the gas reservoir in the very short time interval required for ensuring the safety of the vehicle occupants, explosive arrangements have been employed in the prior art for bursting a diaphragm or cutting through a structural portion of the reservoir. Such explosive arrangements have significant inherent safety problems, such as the production of shrapnel by the explosion, as well as the relatively high sound level reached within the passenger compartment due to the explosion. The psychological factor of having these explosives in each automobile also cannot be ignored.
The second technique discussed above employs a pyrotechnic gas generator, or explosive gas generator, having a rapidly burning propellant composition stored therein for producing substantial volumes of hot gaseous products which are then directed into the inflatable bag. Some compositions are available which produce a sufficiently low temperature combustion gas such that the gas may be substantially directed into the bag without danger to the vehicle""s occupants. Other systems produce a high temperature combustion product requiring means for cooling the gas before it is introduced into the bag.
Many forms of gas generators or inflators utilizing combustible solid fuel gas generating compositions for the inflation of crash protection, i.e., xe2x80x9cairbagxe2x80x9d, restraint systems are known in the prior art. Commonly encountered features among generators utilized for this purpose include: (1) an outer metal housing, (2) a gas generant composition located within the housing, (3) means to ignite the gas generant responsive to a signal received from a sensor positioned at a location removed from the inflator, and (4) means to filter and to cool the gas, positioned between the propellant composition and a plurality of gas discharge orifices defined by the generator housing.
One such gas generator includes an annular combustion chamber which is bounded by a welded outer casing or housing structure. The combustion chamber encloses a rupturable container or cartridge that is hermetically sealed and which contains a solid gas generant in pelletized form, surrounded by an annular filter assembly. The device further includes a central ignition or initiator zone and a toroidal filter chamber adjoining and encircling the combustion chamber. An inner casing or housing structure is located in close surrounding and supporting relationship to the rupturable container, the inner casing being formed by a cylinder having uniformly spaced peripheral ports or orifices near one end. These orifices provide exit holes to facilitate the flow of gas from the combustion chamber.
EP-0842828A1 discloses an apparatus for enhancing the operation of an airbag generator based on the use of an explosive device combined with an oxide or zeolite molecular sieve which is coated or applied to the interior surface of a chamber containing stored gas to assist in supplying gas to the airbag in the final phase of the airbag deployment.
Pyrotechnic devices generate gases at high temperatures and produce potentially toxic materials. It is an objective of the present invention to reduce the amount of toxic gases generated during the deployment of an airbag to protect the occupant or driver of the vehicle.
It is an objective to reduce the potential hazard to a driver or passenger of a vehicle employing passive restraints by reducing the temperature of the gases generated by a pyrotechnic inflator.
It is an objective of the present invention to provide a safe method of storing gas and to provide a process for scavenging of toxic gases generated in the deployment of an airbag system.
The present invention provides two novel improvements to airbag inflators of the prior art to significantly reduce the potential hazard to the driver or passenger of the vehicle. By the pre-loading of the molecular sieve zeolites with gases such as air, nitrogen, or carbon dioxide, the invention provides for rapid airbag inflation by the rapid desorption of this pre-loaded gas. This additional amount of gas evolved reduces the amount of explosive required to inflate the bag which reduces the amount of toxic gases generated by the explosion itself, and the expansion of the stored gas provides a substantial amount of cooling. Following the evolution of the stored gas and combined with the heat provided by the explosion, the adsorbent is now in an activated form and moving freely, or fluidized, within the airbag. It is at this point, the adsorbent additionally provides the remediation of toxic waste gases generated by the exploding inflator device. Molecular sieve zeolites, particularly zeolite X, having been exchanged with lithium or calcium provide both high-capacity gas storage and enhanced toxic waste gas adsorption. The use of molecular sieve zeolites reduces risk of injury to occupants of vehicles from exposure to hot, toxic waste gases following airbag deployment.
In one embodiment, the present invention is an explosive airbag inflator comprising a pyrotechnic to produce a generated gas and a zeolite molecular sieve which was pre-loaded with a stored gas. The generated gas comprises toxic compounds. The zeolite molecular sieve is disposed in a zeolite layer adjacent to the pyrotechnic. Upon detonation, a sufficient amount of zeolite molecular sieve is present to reduce the temperature of the generated gas and to scavenge at least a portion of the toxic compounds passed to the airbag.
In another embodiment, the present invention is an explosive airbag inflator comprising a cup having a hollow interior and an open end, a layer of pyrotechnic disposed in the hollow interior, a layer of zeolite molecular sieve pre-loaded with nitrogen or carbon dioxide and disposed on the layer of pyrotechnic, and a membrane or rupture disk disposed over the layer of zeolite molecular sieve.
In a further embodiment, the present invention is a process for reducing the temperature of an inflating airbag. The process comprises the steps of detonating an airbag inflator comprising a pyrotechnic adjacent to a zeolite molecular sieve. The molecular sieve was pre-loaded with a stored gas. The pyrotechnic provides a generated gas which comprises toxic compounds. The stored gas from the zeolite molecular sieve is desorbed and expanded in the detonation to cool the generated gas and to fluidize at least a portion of the zeolite molecular sieve. At least a portion of the toxic compounds is adsorbed on the zeolite molecular sieve.